1. Field of the Invention
The present invention relates generally to oscillating laser light sources. More particularly, the present invention relates to an apparatus and method for producing an amplified rapidly oscillating laser light source which exhibits substantially uniform gain during each pulse with improved efficiency and extended pulse duration. Further, the present invention relates to a method of using the unique rapidly oscillating light source in producing an image or other applications.
2. Related Art
Producing a rapidly oscillating laser light has many potential uses, particularly in producing visual displays, medicine, dentistry, pulse formation, and in communications. One method of producing an oscillating light source is field or color sequential methods. These devices can use a rotating filter of red, blue, and green in front of a projection tube and detecting the color of the projected light to electronically switch the appropriate color input to the projection tube. U.S. Pat. Nos. 4,197,559 and 4,582,396 describe such a system.
Early lasers operated only by pulsing, however such systems require pumping using a flash lamp or similar device which takes time to recharge between pulses. Other methods have used an array of laser diodes which are directly pulsed. Another method is to intermittently disrupt the ability of a laser cavity to resonate. When resonance is restored to the cavity, the energy previously pumped into the cavity is released producing a high power oscillating laser light, often referred to as Q-switching. The resulting pulsed light is often limited to about 50 kHz and has a peaked output signal of short duration with essentially uncontrollable pulse duration. U.S. Pat. No. 3,818,129 describes using rotating mirrors in a Q-switch to produce a color image from three laser light sources.
One of the more recent methods for producing oscillating light includes mode locking. Mode-locked lasers have an absorber placed in the laser cavity which interacts to select preferred modes of oscillation. Upon removal of the absorber the signal and its harmonics are summed. The absorbers are chosen for very specific conditions and make control over a wide range of conditions difficult. Such lasers produce short duration pulses of essentially uncontrollable pulse width at pulse repetition frequencies near 100 MHz. Further, to obtain wavelengths useful in optical display systems would require extraordinarily long cavities of hundreds of meters.
Laser amplifiers are important in producing a laser output at power levels desirable for many applications. One difficulty with many laser fiber amplifiers is that the amplifier gain depends on the power and duration of the incoming light. Particularly, with fiber amplifiers the gain decreases as the input power increases. Further, due to population inversion effects in the amplifier the gain is higher at the beginning of a constant pulse and decreases during the pulse. Several methods have attempted to overcome these problems with varying degrees of success.
In one method of controlling amplifier output, the input and output signals are compared. Based on this comparison the amplifier pump source is adjusted to hold the gain constant. At high pulse speeds, the response of the amplifier may be slower than the pulses. U.S. Pat. 5,633,750 describes a method of rapidly controlling amplifier gain without an input signal which avoids this problem.
Some attention has been spent on pulse shaping and various methods for controlling signal characteristics for ultra-fast laser pulsing systems. Particularly, research on Q-switch laser systems has attempted to improve pulse shape control by various methods including pulse slicing which involves substituting select time intervals of the laser light to produce the desired output. Another variation is to truncate the xe2x80x9ctailsxe2x80x9d of a Gaussian beam to achieve sharp rise times and a narrow pulse, which results in dramatic energy losses and decreased efficiency. Q-switch methods currently do not provide an efficient pulsed laser light source having desirable pulse shape characteristics for use in technologies such as is required in color display systems.
Further, a desirable improvement in the art would be to provide a method of achieving a rapidly oscillating light source having an amplified pulse shape which is substantially rectangular.
It has been recognized that it would be advantageous to develop a rapidly oscillating light source for use in producing visible light which has a controlled pulse intensity, duration and sharp rise and fall times to produce a substantially rectangular pulse.
The present invention provides a rapidly oscillating laser light source for use in image display systems which includes at least; a pulsed laser light source configured to generate a pulsed beam of light having a predetermined wavelength, frequency, and controlled pulse shape; a fiber amplifier connected to the pulsed laser light source for amplifying the intensity of the pulsed beam of light; and a control system operatively coupled to both the pulsed laser light source and the amplified output. The control system is configured to measure the amplified output and adjust the pulse shape produced by the pulsed laser light source in order to compensate for changes in amplifier gain during each pulse, to produce substantially uniform amplified output.
In accordance with a more detailed aspect of the present invention, the system may include a nonlinear resonator for frequency conversion or mixing to produce laser light in the visible range.
In accordance with another more detailed aspect of the present invention, the system may use a rapid feedback system to adjust the light source and maintain resonant conditions in the laser cavity.
In accordance with yet another more detailed aspect of the present invention, the system may comprise using multiple oscillating laser light sources produced using the method of the present invention to produce an image for use in display systems.